1. Field of the Invention
The present invention relates to a display panel having a multilayer structure including a colored glass layer and a non-colored glass layer and to a process for manufacturing the display panel.
The display panel utilizes a structure having a glass layer with a coloring agent disposed on the inner face of a substrate as a stripe-like or a grid-like light shield member for enhancing contrast or a filter for color reproduction.
2. Description of the Prior Art
An AC type gas discharge display panel (i.e., a plasma display panel) has a dielectric layer that insulates electrodes arranged on the inner surface of the substrate from the discharge space. In general, the dielectric layer is made of a low melting point glass and is spread over the whole screen uniformly. The colored glass layer of a predetermined color is overlayed by the dielectric layer (as an under coat, for example). Namely, a multilayer structure including a colored glass layer and a non-colored glass layer is formed on the substrate. A thick layer method is used for forming the multilayer structure, in which glass paste is coated and burned.
The dielectric layer is preferably burned at the temperature substantially higher than the softening point of the glass material. However, if it is burned at the temperature approximately 100 degrees centigrade higher than the softening point, flow of the glass may cause a pattern collapse of the colored glass layer, diffusion of the coloring agent into the dielectric layer resulting in deterioration of transparency of the dielectric layer, or color change of the coloring agent resulting failure in obtaining desired coloring effect. Therefore, conventionally, the composition of the glass material of the dielectric layer is selected so that the softening point becomes a relatively high temperature (e.g., 570 degrees centigrade), so that the burning is performed at a temperature (e.g, 590 degrees centigrade) that is near to the softening point. In addition, in order to obtain a good dielectric layer, a thin dielectric layer is formed on the colored glass layer using a glass material having high softening point, and then, a material having low softening point (e.g., 490 degrees centigrade) is used and is burned at substantially high temperature so that the dielectric layer having a necessary thickness can be formed. The thin dielectric layer can prevent the deformation of the colored glass layer and the diffusion of the coloring agent.
There is another problem if the electrode is made of a transparent conductive material (ITO, NESA). Namely, a metal oxide added as a coloring agent degenerates and causes the color change or fading of the colored glass layer. One of the methods to solve this problem is disclosed in Japanese unexamined patent publication No. 9-129142. The method includes the steps of providing a gap for preventing color change between the transparent electrode and the colored glass layer, and mixing an oxidation agent into the colored glass paste.
If the dielectric layer is formed by the method explained above in which the glass material is burned at the temperature that is close to the softening point, leveling and defoaming process in the softened state can be insufficient so that the surface layer becomes rough with many foams. This layer has little transparency and deteriorates the intensity. The method of coating the thick dielectric layer over the thin dielectric layer can improve the transparency but has a disadvantage in its low productivity since two burning steps are required. In addition, two materials are necessary for the dielectric layer.
Furthermore, in order to avoid the color change and the color fade, the method of providing the gap for preventing color change has a strict limitation for the arrangement pattern of the colored glass layer, while the method of adding the oxidation agent is limited to a special coloring agent.